As the semiconductor device described above, a device described, for example, Patent Document 1 is already known. In the following description of the background art, reference numerals or names used in Patent Document 1 are stated and cited in parentheses where appropriate. In the device described in Patent Document 1, a first base (a case frame 20) to which element units (switching element power modules Ug and Um) are fixed, a second base (a bracket 23) to which a condenser (a smoothing condenser C) is fixed, and a third base (a bracket 24) to which a control board (Uc) is fixed, are arranged so as to be sequentially stacked in a height direction as shown in FIG. 1 of the Document, thereby reducing a size of the device.
The device described in Patent Document 1 has a configuration in which the element units are cooled by arranging the element units so that the element units abut on a bottom wall of the first base (a heat sink H), as described in the paragraph 0042 of the Document. In order to cool the element units efficiently, a configuration is adopted in which the element units are directly fixed to the bottom wall, as described in the paragraph 0034 in the Document, so that the element units come into close contact with the bottom wall of the first base.
However, in Patent Document 1, there is no specific description regarding how to fix the element units to the first base. Therefore, with the configuration of Patent Document 1, depending on a fixation structure of the element units, it is possible to cool the element units efficiently but the size of the device is likely to increase.